Zelda II: The Adventure of Link (1988) did the unthinkable: it threw out almost everything from the first game. Instead of a top-down quest, you get a side-scrolling action-RPG with experience points, magic spells, towns full of NPCs, and a stamina-draining combat system built on up-and-down sword thrusts.

The structure is stranger than people remember. There's still an overworld, but it's a top-down travel map where bumping into a wandering enemy drops you into a side-scrolling fight, closer to an RPG's random encounter than to anything in the first game. Experience pools into three separate tracks you choose between when you level: Attack, Magic, and Life. Spend it on Magic and you can afford the spells; spend it on Life and you survive Death Mountain. It is the only Zelda with lives, a Game Over screen, and a real build decision.

Combat rewards patience in a way no other Zelda does. Enemies block high or low and shift their guard while you watch, so a fight against a single Iron Knuckle becomes a small duel: crouch, thrust low, back off, wait for the shield to move. Once Link learns the downward thrust from the old man in the cave, the whole game opens up, because now you can attack in the middle of a jump and bounce off whatever you hit.

It's hard. Death Mountain alone has ended countless quests, the palaces stack up in difficulty, and the Great Palace at the end is a marathon with Dark Link waiting at the finish. Fans were split then and still are now.

It's also where Link learned that downward thrust, where Dark Link first appeared, and where a townsperson delivered the immortal line "I AM ERROR." That one isn't even a translation bug: the character is named Error, and another town holds a man named Bagu, which is how "bug" comes out in Japanese. Someone at Nintendo was having a good time.

A weird, brave, fascinating sequel, and one the series quietly kept borrowing from for decades.